Many forms of such cutters incorporate a reel on which the flexible filament is wound and from which the actual cutting length extends. During use, the cutting length becomes worn and ultimately breaks at some point along its length and it is then necessary to withdraw a further length of filament from the reel to restore the cutting length to its original value. The withdrawal of filament from the reel can be effected manually but, in many cases, a mechanism controlled by the user is provided. The mechanism, when actuated by the user, allows a controlled length of filament to be withdrawn from the reel by the action of centrifugal force or by the feeding action of a rotatable reel.
The mechanism may be mounted upon a shaft carrying, at one end, a rotatable head which, in use, rapidly rotates the cutting length, and at the other end, a carrying handle by which the user supports and guides the cutter. In such a case, the filament, after leaving the reel, passes down the shaft to the head via a passage through the armature shaft of an electric motor. The head is directly attached to the shaft and includes a passageway that extends radially outwards from the axis of rotation of the shaft. This construction is expensive to produce and requires that the head shall rotate at the same speed as the motor.